Esophageal squamous cell carcinoma (SCC) is a common and deadly disease that kills >400,000 people worldwide each year. A major barrier to improved outcomes is the lack of mechanistically-based (i.e., targeted) therapies. Through studying the role of the transcription factor oncogene SOX2 in esophageal SCC, we propose to advance our mechanistic understanding of this disease and identify new potential therapeutic vulnerabilities. We will follow upon our recent discovery that developmental transcription factor SOX2 is an oncogene subject to amplification or overexpression in the majority of esophageal SCCs. SOX2 is not only selectively subject to genomic amplification in SCCs but it is also essential for the normal development and proliferation of the esophageal squamous epithelium, suggesting a connection between the squamous cell carcinogenesis and transcriptional programs that maintain the squamous esophageal lineage. More recently, we found a novel physical and function interaction of SOX2 with the squamous transcription factor p63, specifically the oncogenic ?Np63 isoform. Our discovery of this SOX2/p63 complex in SCC, we hypothesize, reveals a master transcriptional regulatory complex controlling survival and proliferative programs in the squamous lineage, programs frequently hijacked by SCCs. Additionally, our results suggest a new mechanism by which SOX2/p63 promotes SCC. We found that SOX2 and p63 jointly regulate factors promoting oncogenic signaling including ETV4, AP-1 transcription factors FOS and JUN and their activator, HRAS. Our results further suggest another mechanistic hypothesis for SOX2 activity in cancer, that AP-1 factors further interact with SOX2 to regulate gene expression in SCC. Our proposed focused inquiry into the activity of SOX2/p63 and SOX2/AP-1 provides an opportunity to identify squamous-specific SOX2 functions and mechanisms of SCC, leading to the identification of new candidate vulnerabilities in these tumors In Aim 1, we propose test our hypothesis that p63 is essential for the oncogenic function and activity of SOX2 in esophageal SCC carcinogenesis in vivo and in cultured cells. We will test the effects of loss of p63 upon SOX2 functions in both in vitro and in vivo models. Furthermore, we will jointly analyze experimental data on SOX2/p63 activity in SCC model systems with data on primary patient data from The Cancer Genome Atlas and systematically interrogate lead candidate SOX2 targets to identify novel dependencies in these cancers. In Aim 2 we propose to test our mechanistic hypotheses by charactering the interaction of SOX2 with AP-1 factors and delineating the joint functions of SOX2 with AP-1 factors in SCC. Overall, this research contributes to public health by greatly expanding our understanding on the mechanisms of an oncogene recurrently amplified a set of common and deadly cancers that have sparse effective therapies. This work is designed to specifically enhance understanding of the driving mechanisms of these cancers thus allowing us to ultimately develop more effective targeted therapies.